From US 2014/0026829 A1 a system is known for the liquid cooling of an internal combustion engine with a cylinder head with an integrated water jacket, and a cylinder block with an integrated water jacket. A valve with a rotary slide which in a first operating position separates a first return pipe between the cylinder head water jacket and the valve, in which a heat exchanger is arranged, from a supply pipe between the valve and the water jacket in which a pump is arranged, and connects a second return pipe between the combustion chamber water jacket to the valve and the by-pass pipe connected in parallel to the heat exchanger with the supply pipe. In a second operating position, the valve separates the by-pass pipeline from the cylinder head water jacket from the supply line and connects first and second return pipelines to the supply pipe.